1. Field of the Invention
The present invention relates to a substrate transport apparatus and, more particularly, to a semiconductor substrate transport apparatus with an active edge gripping end effector.
2. Brief Description of Earlier Related Developments
Integrated circuits are produced from wafers of semiconductor substrate material, such as silicon. Multiple integrated circuits are produced from each wafer. The typical fabrication facility is highly automated and uses substrate transport apparatus to transfer substrate wafers composed of partially fabricated integrated circuits between various fabrication tools.
To minimize defects in the integrated circuits, fabrication is carried out in clean rooms where specialized purification systems are employed to remove particle contaminates from the air and safeguards are used to prevent the creation of such contaminates. Dislocation of substrates during transport can cause particle contamination if the dislocated substrate strikes or rubs against another surface. In addition to damaging the dislocated substrate, other substrates can become contaminated with particles created due to the abrasion. Substrate transport apparatus with passive end effectors rely on friction between the end effector and the substrate to prevent dislocation, and therefore have lower operating speeds limited by the coefficient of static friction associated with the material of the passive pads (e.g. elastomeric material for low temperature conditions, or stainless steel, alumina, or quartz for high temperature conditions). Higher speeds are obtained by transport apparatus having active grip end effectors that apply a clamping force to the edge of a substrate as it is moved. Higher transport speeds are desired in the fabrication facility in order to increase production throughput.
Semiconductor substrate transport apparatus often operate within a chamber isolated to hold a controlled atmosphere, such as an inert gas or a vacuum. For example, a conventional substrate processing apparatus may comprise a vacuum chamber (or other chamber capable of holding an isolated atmosphere) with one or more processing modules capable of communicating with the chamber, and at least one load lock chamber to interface with the atmospheric environment outside. The apparatus further conventionally comprises a substrate transport apparatus with a movable arm for transporting substrates between the load lock chamber(s) and the processing modules, the arm being inside the vacuum chamber. It is desirable to use active edge grip end effectors on the transport apparatus for the above stated reasons. Active grip end effectors may employ a source of power and control to operate. In conventional transport apparatus cables extending through the apparatus to the end effector may be used for power or communication. Flexing of cables due to articulation of the transport apparatus can generate contamination particles, the insulation may give off unwanted gasses in a vacuum, and the cables must be adequately sealed where penetrating the chamber to maintain isolation of the controlled atmosphere. To minimize the length of cable runs and associated problems therewith, some conventional transport apparatus may employ slip rings at articulated joints, which in turn are also subject to particulate contamination generation along slip ring contact surfaces. Furthermore, slip rings are expensive, with a commensurate increase in cost of the transport apparatus. Moreover, the cables and/or conduits providing power and control to the end effector of conventional transport apparatus located in isolatable chambers form physical ties tying the conventional transport apparatus to the otherwise fixed power supply or control source. The corresponding result is that conventional transport apparatus in isolated chambers have a base that is fixed in place or has very limited linear transverse mobility. The exemplary embodiments of the present invention overcome the problems of the prior art as will be described further below.